Armchair



FIG. 1 is a front and right side perspective view of an exemplary armchair showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a right side elevation view thereof, the left side being a mirror image;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a rear elevation view thereof.

The broken lines show environmental subject matter and form no part of the claimed design. 

CLAIM The ornamental design for an armchair, as shown and described. 